What is being oxidized, explain why

Hi, nertigo! So a good way to learn oxidation reduction is OIL RIG: Oxidation Is Losing electrons, and Reduction Is Gaining electrons. So, we need to look to see what is losing electrons.

So, Bromine (2Br2) is LOSING electrons (OIL = oxidation) because it is binding to sodium in the product (NaBr) and Hydrogen (HBr). When sodium and hydrogen bind, it occupies the space that use to be filled with electrons.